The following text uses the following definitions:                “meridian plane”: a plane containing the axis of rotation of the tire.        “equatorial plane”: the plane passing through the middle of the tread surface and which is perpendicular to the axis of rotation of the tire.        “radial direction”: a direction perpendicular to the axis of rotation of the tire.        “axial direction”: a direction parallel to the axis of rotation of the tire.        “circumferential direction”: a direction perpendicular to a meridian plane.        “radial distance”: a distance measured perpendicular to the axis of rotation of the tire and from the axis of rotation of the tire.        “axial distance”: a distance measured parallel to the axis of rotation of the tire and from the equatorial plane.        “radially”: in a radial direction.        “axially”: in an axial direction.        “radially inside/radially outside”: the radial distance of which is smaller/larger.        “radially closest to/radially furthest from”: the radial distance of which is minimal/maximal.        “axially inside/axially outside”: the axial distance of which is smaller/greater.        “axially closest to/axially furthest from”: the axial distance of which is minimal/maximal.        
A radial tire more specifically comprises a reinforcement comprising a crown reinforcement, radially on the inside of the tread strip, and a carcass reinforcement radially on the inside of the crown reinforcement.
The carcass reinforcement of a radial tire comprises a plurality of reinforcing elements, usually organized in a single layer, particularly in the case of metal reinforcing elements. These reinforcing elements are parallel to one another and make an angle of between 85° and 95° with the circumferential direction. The carcass reinforcement comprises a main part connecting the two beads to one another and which is wrapped within each bead around a bead wire core. A bead wire core comprises a circumferential reinforcing element, usually made of metal, surrounded by at least one other material: nonexhaustively this might be a polymer material or a textile material. The carcass reinforcement is wrapped around the bead wire core from the inside of the tire toward the outside to form a turned-back portion comprising a free end. Turning the carcass reinforcement back within each bead anchors the carcass reinforcement to the bead wire core of the bead.
It is also known practice for each bead to contain an additional reinforcement consisting of at least one layer of reinforcing elements, which is adjacent to at least part of the carcass reinforcement.
The carcass reinforcement or additional reinforcement reinforcing elements, in the case of a tire for a heavy goods vehicle, are usually metal cords. However, reinforcing elements consisting of collections of textile filaments, preferably made of aliphatic polyamides or of aromatic polyamides are also conceivable. In the case of reinforcing elements consisting of collections of textile filaments, the carcass reinforcement usually comprises several layers of reinforcing elements, the number of which is determined according to the level of mechanical strength required of the carcass reinforcement.
Each bead comprises a filler profiled element extending the bead wire core radially outwards. The filler profiled element has, in any meridian plane, a triangular cross section and is formed of at least one polymer material. The filler profiled element may be formed of a stack in the radial direction of at least two polymer materials in contact along a contact surface that intersects any meridian plane along a meridian line. The filler profiled element axially separates the main part of the carcass reinforcement and the turned-back portion or the additional reinforcement.
A polymer material, after curing, is mechanically characterized by its elastic stresses and its rupture properties, which are determined by tensile testing. This tensile testing is carried out by the person skilled in the art in accordance with a known method, for example in accordance with French standard NF T 46-002, September 1988. The so-called “nominal” secant moduli (or apparent stresses, in MPa) or the so-called “true” secant moduli (in this case with respect to the actual cross section of the test specimen) at 10% elongation (denoted respectively “M10” and “E10”), at 100% elongation (denoted respectively “M100” and “E100”) and at 300% elongation (denoted respectively “M300” and “E300”) are measured in second elongation, which means to say after an accommodation cycle. All these tensile test measurements are carried out under normal temperature (23+ or −2° C.) and hygrometry (50+ or −5% relative humidity) conditions in accordance with French standard NF T 40-101, December 1979. The stresses at rupture (in MPa) and the elongations at rupture (in %) are also measured at a temperature of 23° C. In this document, the elastic modulus of the polymer material of the filler profiled element means the nominal secant modulus at 10% elongation as defined above.
A polymer material, after curing, is also mechanically characterized by its hardness. The hardness is notably defined by the Shore A hardness determined in accordance with standard ASTM D 2240-86.
In use, the tire is mounted on a mounting rim comprising two rim seats intended to be in contact with the radially innermost parts of the two beads and, axially on the outside of each rim seat, a rim flange that is intended to fix the axial position of the said bead when the tire is mounted and inflated.
During running, the beads of the tire are subjected to bending cycles as they wrap around the rim flanges, that is to say as they partially adopt the generally circular geometry of the said rim flanges. This bending is particularly manifested in the form of variations in curvature combined with variations in the tension in the reinforcing elements present in the beads, particularly those in the main part of the carcass reinforcement, the turned-back portion and the additional reinforcement. In addition, these bending cycles introduce into the polymer materials of the filler profiled element and, more particularly, in the immediate vicinity of the free ends of the turned-back and additional reinforcement reinforcing elements, compressive and tensile loadings which generate stresses and thermomechanical deformations which, over time, are likely to degrade the tire, causing it to need to be replaced.
Documents EP 0 826 524 and EP 0 992 369 have already described, in the case of a radial carcass reinforcement, beads the thermomechanical integrity of which is improved with a view to lengthening the life of the tire. These beads comprise two or three polymer materials in the filler profiled element which have different hardnesses, and of which the relative positions in the bead and the contact surfaces are optimized in order to reduce the stresses and thermomechanical deformations within the bead.
Document U.S. Pat. No. 6,000,452 has also described a bead intended to prevent premature tire degradation. The proposed technical solution is a bead that has two filler profiled element polymer materials of different hardnesses, the polymer material of greatest hardness being adjacent to the bead wire core and having a geometric volume greater than a given percentage of the total geometric volume of the filler profiled element.
Document US 2008/0035261 A1 also describes a bead with extended life. The technical solution proposed is a bead that has two filler profiled element polymer materials with different elastic moduli, the polymer material with the highest modulus being adjacent to the bead wire core and having an L-shaped geometry, for a radial carcass reinforcement layer wrapped around the bead wire core with different types of turn-back.